# Django 2.0.dev20170216164632 documentation

# Django 1.5.3 release notes

September 10, 2013

This is Django 1.5.3, the third release in the Django 1.5 series. It addresses one security issue and also contains an opt-in feature to enhance the security of `django.contrib.sessions`.

## Directory traversal vulnerability in `ssi` template tag

In previous versions of Django it was possible to bypass the `ALLOWED_INCLUDE_ROOTS` setting used for security with the `ssi` template tag by specifying a relative path that starts with one of the allowed roots. For example, if `ALLOWED_INCLUDE_ROOTS = ("/var/www",)` the following would be possible:

    {% ssi "/var/www/../../etc/passwd" %}

In practice this is not a very common problem, as it would require the template author to put the `ssi` file in a user-controlled variable, but it’s possible in principle.

## Mitigating a remote-code execution vulnerability in `django.contrib.sessions`

`django.contrib.sessions` currently uses `pickle` to serialize session data before storing it in the backend. If you’re using the signed cookie session backend and `SECRET_KEY` is known by an attacker (there isn’t an inherent vulnerability in Django that would cause it to leak), the attacker could insert a string into his session which, when unpickled, executes arbitrary code on the server. The technique for doing so is simple and easily available on the internet. Although the cookie session storage signs the cookie-stored data to prevent tampering, a `SECRET_KEY` leak immediately escalates to a remote code execution vulnerability.

This attack can be mitigated by serializing session data using JSON rather than `pickle`. To facilitate this, Django 1.5.3 introduces a new setting, `SESSION_SERIALIZER`, to customize the session serialization format. For backwards compatibility, this setting defaults to using `pickle`. While JSON serialization does not support all Python objects like `pickle` does, we highly recommend switching to JSON-serialized values. Also, as JSON requires string keys, you will likely run into problems if you are using non-string keys in `request.session`. See the Session serialization documentation for more details.